• John Stultz's avatar
    RTC: Rework RTC code to use timerqueue for events · 6610e089
    John Stultz authored
    This patch reworks a large portion of the generic RTC code
    to in-effect virtualize the rtc interrupt code.
    
    The current RTC interface is very much a raw hardware interface.
    Via the proc, /dev/, or sysfs interfaces, applciations can set
    the hardware to trigger interrupts in one of three modes:
    
    AIE: Alarm interrupt
    UIE: Update interrupt (ie: once per second)
    PIE: Periodic interrupt (sub-second irqs)
    
    The problem with this interface is that it limits the RTC hardware
    so it can only be used by one application at a time.
    
    The purpose of this patch is to extend the RTC code so that we can
    multiplex multiple applications event needs onto a single RTC device.
    This is done by utilizing the timerqueue infrastructure to manage
    a list of events, which cause the RTC hardware to be programmed
    to fire an interrupt for the next event in the list.
    
    In order to preserve the functionality of the exsting proc,/dev/ and
    sysfs interfaces, we emulate the different interrupt modes as follows:
    
    AIE: We create a rtc_timer dedicated to AIE mode interrupts. There is
    only one per device, so we don't change existing interface semantics.
    
    UIE: Again, a dedicated rtc_timer, set for periodic mode, is used
    to emulate UIE interrupts. Again, only one per device.
    
    PIE: Since PIE mode interrupts fire faster then the RTC's clock read
    granularity, we emulate PIE mode interrupts using a hrtimer. Again,
    one per device.
    
    With this patch, the rtctest.c application in Documentation/rtc.txt
    passes fine on x86 hardware. However, there may very well still be
    bugs, so greatly I'd appreciate any feedback or testing!
    Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
    LKML Reference: <1290136329-18291-4-git-send-email-john.stultz@linaro.org>
    Acked-by: default avatarAlessandro Zummo <a.zummo@towertech.it>
    Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
    CC: Alessandro Zummo <a.zummo@towertech.it>
    CC: Thomas Gleixner <tglx@linutronix.de>
    CC: Richard Cochran <richardcochran@gmail.com>
    6610e089
rtc-lib.c 3.29 KB